1. Field of the Invention
The present invention relates to a semiconductor device for charge-up damage evaluation and a charge-up damage evaluation method for use during steps of manufacturing semiconductor devices.
2. Description of the Related Art
As patterns of elements have become finer and denser, gate oxide films and wires of MOS transistors and the like are becoming finer. Hence, it is increasingly important to prevent damage upon an oxide film owing to charge-up during a semiconductor manufacturing process. Charge-up damage upon a thin oxide film during an ion beam irradiation process, such as ion implantation, or at a dry etching step using plasma has been a problem, and therefore, an antenna-mounted MOS (Metal Oxide Semiconductor) capacitor as that shown in FIG. 11 has been used for evaluation of charge-up damage (See Japanese Patent Application Laid-Open Gazette No. H8-203971 (pages 2 to 3) for instance.).
In FIG. 11, denoted at 101 is a silicon substrate, denoted at 102 is a thin-film gate oxide film which will serve as a capacitor area, denoted at 103 is an element isolation oxide film, and denoted at 104 is a polysilicon film which will serve as an antenna electrode. In an antenna-mounted MOS capacitor structure, the element isolation oxide film 103 is formed on the silicon substrate 101, the thin-film gate oxide film 102 is then deposited, and the polysilicon film 104 is deposited on the entire surface. In general, an antenna-mounted MOS capacitor comprises at a logarithmic ratio a plurality of capacitors whose antenna ratio:A (A=antenna electrode surface/capacitor surface) varies from 1 to 106 times.
In a method of evaluating charge-up damage in this antenna-mounted MOS capacitor, the antenna-mounted MOS capacitor is processed by ion implantation or the like and a voltage is then applied upon an insulation film of the MOS capacitor to thereby apply electric stress, a voltage which develops upon dielectric breakdown of the insulation film is measured, a chip which is at or below a certain threshold voltage (which is 8 MV/cm for instance) is identified as a defect, and a ratio of failing capacitors (destruction of the gate oxide film) is calculated. A process condition is set such that the antenna-mounted MOS capacitor will not be destroyed.
However, the conventional antenna-mounted MOS capacitor for charge-up damage evaluation described above has a problem that while it has high sensitivity to damage upon the thin-film gate oxide film 102 attributed to direct charging with electric charges associated with ion implantation, plasma etching, an electron ray and the like, the sensitivity to static electricity developed by frictions and the like is low. During ion implantation, etc., a large electric field is applied upon the antenna electrode. When the applied electric field is uneven, the applied electric field makes a current flow in the thin-film gate oxide film 102. Since a large amount of electric charges pass through the thin-film gate oxide film 102 at this stage, the thin-film gate oxide film 102 is destroyed.
Although a large electric field is applied upon the antenna electrode because of static electricity which develops by frictions between insulation members or the like, the amount of electric charges is extremely small, and hence, there will be no flow of electric charges (current) which is large enough to destroy the thin-film gate oxide film 102. For this reason, the sensitivity of the conventional antenna-mounted MOS capacitor to charge-up damage owing to static electricity is low.